yes, i understand, but that's not really what i was getting at. what i meant was, should the differences in systems be a factor in choosing between a shorty or full length AR. as in: do shorty's heat up faster under sustained shooting? is the gas pulse stronger with a shorty since it's vented closer to the chamber? if so, is that good or bad?

Originally Posted By USMCsilver:Umm, the reason the 16" sysetm is shorter is because the barrel is shorter...

You cannot use a 16 in a 20 and you cannot use a 20 in a 16.

Get it?

His question seemed fairly straight forward to me. Anyway, rtl, although my experience is somewhat limited, and some would probably disagree with me, I would say there are more reliability issues with a 16" gas system. The heating up factor should not be an issue, unless you are shooting burst/full auto. However, the higher pressure gas pulse can be more prone to failure to extract/eject issues among others. Of course, saying this, I own two Bushmaster 16" carbines. I just got my second recently, and am currently having a failure to eject issue with it. Im hoping its just a faulty extractor or spring. I have been told that FTE's occur more in 16" because of the higher gas pressure which causes the bolt to be driven back more viloently than on a 20". Anyway, hope that helps.

The 16 inch has a more reliable gas system, in country boy terms, The 16 inch gets more "gas time" to operate the system. The M4 has the same "gas time" as thr 20 inch models, I invented the word "gas time" Def is the amount of time after the bullet passes the gas port and before the bullet leaves the barrel.

Anything with the carbine system will have a shorter elapsed time until the gas hits the bolt carrier and begins the cycling process than rifle gas system will. That means that pressures will be higher when the extraction process begins, which can lead to extraction problems. That is the primary difference.

The second, but less important issue is the amount of barrel beyond the gas port. There has to be enough barrel to sustain the gas impulse, or not enough gas will be directed to reliably cycle the rifle. This is really only an issue for 10" or 11.5" "carbine system" or 16" "rifle system" guns, because they have such little barrel beyond the gas port. This is why Bushmaster and others add a second gas block at the carbine location for their Dissipator rifles.

rtl,

To answer your question: 20" barrels with the "rifle" gas system will be the most reliable. However, the carbine system has been refined enough that there isn't enough difference that you should choose your rifle's configuration based on them. Instead, you may do better to focus on range issues (i.e., how much barrel you need), weight, and sight configuration, all of which are much more important in the scheme of things.